Method and apparatus for treating objects with gas



Dec. 10, 1968 w. R. KEOUGH METHOD AND APPARATUS FOR TREATING OBJECTS WITH GAS Filed May 24, 1967 INVENTOR.

WILLIAM R. KEOUGH w/Ls0/v, SETTLE, BATCHELDER 8 CRA I6 ATT'YS.

United States. Patent METHOD AND APPARATUS FOR TREATING OBJECTS WITH GAS William R. Keough, Birmingham, Mich., assignor of forty-five percent to Multifastener Company, Detroit, Mich., a partnership Filed May 24, 1967, Ser. No. 640,909 13 Claims. (Cl...34-22) ABSTRACT OF THE DISCLOSURE A method and device for heat treating articles which are moved between inlet and outlet openings along a helical path while being subjected to heated gases. The heated gases are introduced between the inlet and outlet openings and are flowed radially outwardly into the helical path and along the helical path toward the outlet opening. Means are provided for recirculating the heated gases intermediate the inlet and outlet openings by providing a reduced throat to suck gases from the helical path adjacent the outlet opening Objects of the invention It is an object of this invention to provide an improved rotary retort in which a hot gaseous atmosphere is circulated and recirculated over objects to be heat treated as they are turned and tumbled through the retort.

Another object of the invention is to provide a method of treating objects with gas in which the gas is circulated through a rotary retort and over the objects by means of a jet pump including a venturi tube.

A further object of the invention is to provide a method and apparatus for treating objects with gas in which gas is passed through a passageway and is circulated countercurrent to the gas flow in the passageway through an enclosed space outside the passageway back to the entrance of the passageway, so that a continuous circulation and recirculation of gas over objects placed in the enclosed space is provided.

Another object of the invention is to circulate gas in a helical path about the passageway to assure full exposure of the objects to the gas.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

0n the drawings:

FIGURE 1 is an elevational view, partly in section, of a retort assembly which constitutes one embodiment of the invention;

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1; and

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 1.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

As shown on the drawings:

A retort assembly in accordance with one embodiment of the invention includes an elongated tubular casing 12 having end portions at 14 and 16. In the illustrated ice embodiment, end bells 18 and 20 are welded respectively to the opposite ends 14 and 16 of the tubular casing, although it will be understood that the end bells 18 and 20 could be fitted over the ends 14 and 16 of the casing so as to be removable, if desired. End bell 18 narrows down to a neck 22 which is open at end 24, and this allows objects to be treated to be inserted into the retort through the open end 24 of end bell 18. At the other end of the retort, end bell 20 tapers down to a neck 26, and a collar 28 is secured to the neck 26. A stem 30 is inserted into the collar 28 and neck 26, and this stem projects outwardly and terminates in a tip 32 which may be connected to a source of hot gas. The inner end 34 of stem 30 fits within the neck 26 and the collar 28 closely enough to hold the stem 30 in place.

A nozzle tube 38 fits at its right-hand end 40 into the tip 32 of stem 30 and projects from there through the end bell 20 into the space within the casing 12. Nozzle tube 38 terminates in an end 42 from which hot gas emerges as a jet or stream, the hot gas being supplied to the nozzle 38 under pressure.

Within the casing 12 is a tube 44 which provides a passageway leading longitudinally of the casing 12. Tube 44 is mounted coaxially with the casing 12 and the wall of tube 44 is spaced inwardly from the tubular casing 12 to provide a space 46 between the wall of tube 44 and the wall of casing 12.

Tube 44 is supported by and within a helical screw 48 which has flights 50 encircling the tube 44 and extending between the tube 44 and the wall of casing 12. The screw flights 50 are welded to the casing 12 to turn with the casing in the operation of the retort assembly. The screw 48 has an axial opening 52 which extends through its central portion and inwhich the tube 44 is received.

Objects to be treated with hot gas are inserted through the neck 22 of end bell 18 and are placed adjacent the left-hand flight 50' of the screw 48. The casing 12 is then rotated to advance the objects along the length of the tubular casing 12 until the objects are properly positioned within the retort. As the casing 12. is rotated objects are advanced by the helical flights 50 to the right-hand end 16 of the casing 12. An opening 56 is provided at the right-hand end of casing 12, and the objects being treated leave the retort through the opening 56.

The objects to be treated are typically made of steel, although other metal objects might be treated with gas for some applications. The gas which is supplied to the retort through the nozzle tube 38 may be any one of a wide variety of gasses, and the utility of the invention is not limited to any one gas or mixture of gases. For a carburizing treatment, natural gas or methane might be introduced into the retort through nozzle tube 38. For nitriding purposes, ammonia might be included in the incoming gases. In general, any desired gas may be introduced into the retort to provide a controlled atmosphere therein, and the gas might be at any desired temperature. As a typical example, the incoming gas might be at a temperature of about 1700 F.

Located within and near the right-hand end of tube 44 is a venturi tube 60. Venturi tube 60 may be welded at one end 62 to the tube 44, and the other end 64 of venturi tube 60 may have a press fit with the inner wall of the tube 44. Venturi tube 60 has a narrowed down throat portion 66, and the end 42 of nozzle tube 38 is located within or adjacent this venturi throat 66. The venturi tube 60 has a down-stream side 68 which tapers outwardly from the throat 66 and contacts the inner wall of tube 44 at end 64 as already mentioned. The venturi tube 60 also has an up-stream side 70 which tapers outwardly from the throat 66 and also contacts the inner wall of tube 44 at end 62.

The tube 44 has a plurality of openings 74 extending through it at the portion of tube 44 located down-stream from the venturi tube 60. Thus, the down-stream portion of tube 44 communicates with the enclosed space 46 between tube 44 and casing 12. At the right-hand end of tube 44, there are also a plurality of openings 76 through the wall of tube 44 so that the right-hand end of tube 44 located to the right of venturi tube 60 also communicates with the space 46 between tube 44 and the casing 12. It may be seen that the venturi tube 60 communicates with the enclosed spaced 46 at a portion 78 thereof located near the right-hand end of casing 12.

Hot gases entering the retort through nozzle tube 38 pass through the venturi tube 60 into the downstream portion of tube 44. As the gas flows to the left along tube 44, it flows through the openings 74 into the enclosed space 46. As the gas flows through venturi tube 60, a reduced pressure is produced in the throat 66, and as a result of this reduced pressure, gas is sucked from the portion 78 of space 46 into the venturi tube 60, the gas flowing through the openings 76 to the interior of tube 44 and from there into the venturi tube 60. It may be seen that the pressure at the left-hand end of tube 44 is greater than the pressure at the right-hand end of tube 44 due to the reduced pressure produced by the gas flowing through venturi throat 66. Since the venturi tube is in communication with the space 78 through openings 76, there is also a reduced pressure in the space 78. Thus, gas entering the space 46 through openings 44 will flow to the right through space 46 back toward the entrance of the venturi tube 60. The gas flow in space 46 is generally counter-current to the gas flow in tube 44, and it may be seen that a continuous circulation of gas is provided through venturi tube 60, through tube 44 and out into space 46, through space 46 toward the right, and back through openings 76 in tube 44 to the venturi tube 60. The objects placed in the casing 12 are exposed to the gas flowing in space 46, and the treatment is carried out as the gas flows over and in contact with these objects. As in any furnace of this type the parts are turned and tumbled as they are lifted by the helical flights 50 and drop therefrom by gravity.

It will be remembered that the screw 48 is located in a space 46 between the tube 44 and the casing 12. The screw 48 imparts a helical motion to the gas flowing in space 46 so that the gas flows spirally or helically around the tube 44 as it simultaneously flows generally to the right in the enclosed space 46. Thus, the gas flows in a helical path around the tube 44 and back toward the entrance of the venturi tube 60. This, in combination with the turning and tumbling of the objects, assures that the gas will have good wiping contact with the objects placed in the casing 12 and assures that all of the objects will be contacted by the hot gas.

The invention has a method aspect, and the steps of the method are as follows: First, a stream of hot gas is produced, and this may be carried out for example by passing gas under pressure through a nozzle tube such as tube 38. The hot gas stream is directed tthrough a venturi tube such as venturi tube 60 into a passageway such as tube 44 which communicates with an enclosed space surrounding the passageway, the enclosed space being at 46 in the illustrated embodiment. The gas is passed from the passageway to the enclosed space as through openings 74 in tube 44. Simultaneously, gas is sucked from the enclosed space through the venturi tube by means of the reduced pressure produced in the venturi tube by the gas stream or jet. Thus, a circulation of gas is produced through the venturi tube, the passageway and the enclosed space. The objects to be treated are placed in the enclosed space and are exposed to the gas flow therein so that they are treated by the gas, for example for carburizing or nitriding purposes. As a further step, the gas flowing through the enclosed space is directed in a helical path around the passageway and over the objects in the enclosed space to assure full contact between the flowing gas and the objects.

Thus, a retort assembly and method are provided in which gas is continuously recirculated to provide a full flow of gas over the objects being treated. The recirculation is accomplished by a jet pump made up of a venturi tube and a nozzle so that at the same time that gas is being introduced into the enclosed space where the objects are located, gas is also being sucked out of the enclosed space through the venturi tube and fed down a passageway which leads to the enclosed space. Although some gas flows out of the retort, much of the gas is recirculated, so that a continuous recirculating system is provided. This reduces the amount of gas required for treating the objects and assures that the gas flow is utilized efiiciently.

Having thus described my invention, I claim:

1. A retort assembly including in combination, a casing, a tube in said casing having a plurality of openings through the tube wall thereof providing communication between the interior of said tube and a space in said casing outside said tube, means for introducing objects to be treated into the latter space, means within a portion of said tube forming a venturi throat, means for producing a flow of hot gas through said venturi throat into said tube downstream from said throat and through openings in said tube into said space in said casing, the gas flow through said throat producing a reduced pressure therein which sucks gas from the space in said casing upstream from said throat into and through said throat, thus causing hot gas to circulate in one direction through said tube and in the opposite direction through said space in said casing and over objects to be treated when placed in said space, and means in said space outside said tube for directing the flow of gas in said space generally helically around said tube as well as along said tube in the direction opposite to the direction of flow in said tube.

2. The retort assembly as claimed in claim 1 in which said means for directing flow helically comprises a screw having flights encircling said tube and extending longitudinally of said tube in said space.

3. The retort assembly as claimed in claim 2 in which said casing is tubular and concentric with said tube, and in which said screw abuts the inside of said tubular casing and the outside of said tube.

4. A retort assembly for treating metal objects with hot gas comprising a rotatable casing, means supporting said casing for rotation, hollow means in said casing providing a passage for flow of the hot gas and communicating with a space in said casing outside said hollow means, a venturi tube communicating with the interior of said hollow means on a downstream side of said tube and communicating with a portion of said space on an upstream side thereof, and gas issuing means to direct a stream of hot gas through said venturi tube from the upstream side to the downstream side thereof and into said hollow means and from there into said space, the gas flow through said venturi tube producing a reduced pressure therein which sucks gas from said portion of said space into said tube and thereby produces a flow of gas through said space generally counter-current to the gas flow through said hollow means, and means for introducing into and removing from said space the metal objects for exposure to the gas flow therein when the retort assembly is operating.

5. The retort assembly of claim 4 further including means for circulating the gas flowing in said space about said hollow means as well as counter-current to the gas flow in said hollow means.

6. The retort assembly of claim 5 in which said hollow means comprises a tube and said means for circulating gas comprises a helical screw surrounding the latter tube and effective to advance metal objects through said space as said retort is rotated.

7. A retort assembly including in combination, an elongated tubular casing, a first tube in said casing spaced radially from and coaxial therewith, said tube having a plurality of openings through the wall thereof providing communication between the interior of said tube and the space between said tube and said casing, objects to be treated being received within said space, a venturi tube having an upstream side and a downstream side, said venturi tube communicating with the interior of said first tube on said downstream side and communicating with a portion of said space on said upstream side, a gas issuing nozzle adjacent said venturi tube to direct a stream of hot gas through said venturi tube from the upstream side to the downstream side thereof and into said first tube and from there into said space, the gas flow through said venturi tube producing a reduced pressure therein which sucks gas from said portion of said space into said venturi tube and thereby produces a flow of gas through said space generally counter-current to the gas flow through said first tube, and a helical screw in said space and encircling said first tube for directing the flow of gas in said space helically around said first tube as well as generally counter-current to the flow of gas in said first tube, the objects in said space being exposed to the gas flow therein when the retort assembly is operating.

8. In a method of treating objects with gas, the steps of producing a stream of gas, directing the gas stream into a passageway communicating with an enclosed space surrounding said passageway, reducing the pressure of said gas stream at a region near or at the entrance to said passageway where said region communicates with said enclosed space, passing the gas from said passageway to said enclosed space, sucking gas from said enclosed space into said passageway at said region by means of the reduced pressure therein, thereby providing a recirculation of hot gas through said passageway and said enclosed space, introducing objects to be treated into said enclosed space, and turning and tumbling the objects in said space for exposure to said flowing gas.

9. In a method of treating objects with hot gas in a rotatable heat treat furnace having spaced inlet and outlet openings, the steps of issuing a stream of hot gas from a nozzle, passing the gas of said stream into a central passageway communicating with an enclosed coaxial space outside said passageway, passing the gas from said passageway to said enclosed space, said space defining a helical path through which the gas flows, and removing gas from said helical path into said central passageway by means of the reduced pressure produced in said passageway by said gas stream, thereby producing a flow of gas through said enclosed space generally counter-current to the flow of gas in said passageway, the objects to be treated being placed in said enclosed space and exposed to said gas flow therein as they are advanced from said inlet opening to said outlet opening by rotation of said furnace.

10. In a method of treating objects with hot gas, thr steps of producing a stream of hot gas, directing said ga: stream through a venturi tube into a hollow means com municating with an enclosed space outside said hollow means, said venturi tube also communicating with sair enclosed space on the upstream side of said tube, passing the gas from said hollow means to said enclosed spacr directing the gas flowing in said enclosed space in a gen erally helical path about said hollow means and over said objects, and sucking gas from said enclosed space through said venturi tube by means of the reduced pres sure produced in said venturi tube by said gas stream thereby producing a circulating of gas through said ven turi tube, said hollow means and said space, the object: to be treated being placed in said enclosed space and ex posed to the gas flow therein.

11. In an apparatus for treating articles with heater gases and including means defining a chamber having spaced inlet and outlet openings for said objects, anc means defining a helical path between said inlet and out let openings for the movement of said articles within saic chamber, the improvement of means for recirculating the heated gases through said chamber comprising, means for injecting heated gases axially of said helical path anc toward said inlet opening for flow radially into said patl intermediate said inlet and outlet openings, said means defining said helical path directing the heated gase: through at least a portion of said helical path and towarr said outlet opening, and means for utilizing the injectior of heated gases to induce the return of said gases fron said helical path for axial flow toward said inlet opening 12. Apparatus as defined in claim 11, including the further improvement of a tube within said means defining a helical path with said means for injecting heated gase: having an exit intermediate opposite ends of said tube and means defining sets of openings in said tube ant spaced in opposite directions from said exit for allowing flow of heated gases between said helical path and saic tube.

13. Apparatus as defined in claim 12, in which saic means for utilizing the injection of heated gases to induce the return of said gases comprises means defining a restricted throat in said tube between said sets of openings References Cited UNITED STATES PATENTS 12/1946 Doyle.

3/1950 Lykken.

US. Cl. X.R. 34-431; 263-62 

